Mobile communication system and user terminal

ABSTRACT

A first user terminal according to an embodiment comprises: at least one processor and at least one memory coupled to the processor. The processor is configured to perform processes of: determining first radio resources to be used for transmitting control information, the control information indicating location of second radio resources to be used for transmitting data by direct Device-to-Device communication; and directly transmitting the same control information repeatedly to a second user terminal in each resource block included in the first control resources.

RELATED APPLICATIONS

This application is a continuation application of internationalapplication PCT/JP2015/052413, filed Jan. 28, 2015, which claims benefitof U.S. provisional Application No. 61/934,305, filed on Jan. 31, 2014,the entirety of all applications hereby expressly incorporated byreference.

TECHNICAL FIELD

The prevent disclosure relates to a mobile communication system thatsupports D2D communication, and a user terminal thereof.

BACKGROUND

In 3GPP (3rd Generation Partnership Project) which is a project aimingto standardize a mobile communication system, the introduction of Deviceto Device (D2D) proximity service is discussed as a new function afterRelease 12 (see Non Patent Document 1).

The D2D proximity service (D2D ProSe) is a service in which directcommunication is enabled without passing through a network within asynchronization cluster formed by a plurality of synchronized userterminals. The D2D proximity service includes a discovery process(Discovery) in which a proximal terminal is discovered and acommunication process (Communication) in which direct communication isperformed.

PRIOR ART DOCUMENT Non-Patent Document

-   Non Patent Document 1: 3GPP technical report “TR 36.843 V1.0.0” Jan.    16, 2014

SUMMARY

Meanwhile, when a user terminal decides a time-frequency resource(hereinafter, referred to as a data resource, where appropriate) usedfor transmitting D2D communication data, it may be considered that inorder to inform peripheral user terminals of the decided data resource,the user terminal transmits control information indicating a location ofthe decided data resource.

However, a user terminal intended to receive the control information mayhave to scan all time-frequency areas in which a time-frequency resource(hereinafter, referred to as a control resource, where appropriate) usedfor transmitting the control information is likely to be arranged.

Therefore, an object of the present disclosure is to provide a mobilecommunication system and a user terminal with which it is possible toefficiently scan control information.

A first user terminal according to an embodiment, comprises: at leastone processor and at least one memory coupled to the processor. Theprocessor configured to perform processes of: determining first radioresources to be used for transmitting control information, the controlinformation indicating location of second radio resources to be used fortransmitting data by direct Device-to-Device communication; and directlytransmitting the same control information repeatedly to a second userterminal in each resource block included in the first control resources.

An apparatus for a first user terminal according to an embodimentcomprises: at least one processor and at least one memory coupled to theprocessor. The processor configured to perform processes of: determiningfirst radio resources to be used for transmitting control information,the control information indicating location of second radio resources tobe used for transmitting data by direct Device-to-Device communication;and directly transmitting the same control information repeatedly to asecond user terminal in each resource block included in the firstcontrol resources.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of an LTE system.

FIG. 2 is a block diagram of UE.

FIG. 3 is a block diagram of eNB.

FIG. 4 is a protocol stack diagram of a radio interface in an LTEsystem.

FIG. 5 is a configuration diagram of a radio frame used in an LTEsystem.

FIG. 6 is a diagram illustrating a data path in cellular communication.

FIG. 7 is a diagram illustrating a data path in D2D communication.

FIG. 8 is a configuration diagram of a radio frame for illustrating amobile communication system according to an embodiment.

FIG. 9 is a configuration diagram of a radio frame for illustrating amobile communication system according to an embodiment.

FIG. 10 is a configuration diagram of a radio frame for illustrating anoperation example 1.

FIG. 11 is a configuration diagram of a radio frame for illustrating amodification of the operation example 1.

FIG. 12 is a configuration diagram of a radio frame for illustrating anoperation example 3.

FIG. 13 is a configuration diagram of a radio frame for illustrating anoperation example 4.

FIG. 14 is a configuration diagram of a radio frame for illustrating theoperation example 4.

FIG. 15 is a configuration diagram of a radio frame for illustrating theoperation example 4.

FIG. 16 is a configuration diagram of a radio frame for illustrating amodification 1 of the operation example 4.

FIG. 17 is a configuration diagram of a radio frame for illustrating themodification 1 of the operation example 4.

FIG. 18 is a diagram for illustrating SIB according to the modification1 of the operation example 4.

FIG. 19 is a configuration diagram of a radio frame for illustrating amodification 2 of the operation example 4.

FIG. 20 is a configuration diagram of a radio frame for illustrating amodification 3 of the operation example 4.

FIG. 21 is a flowchart for illustrating a modification 4 of theoperation example 4.

FIG. 22 is a configuration diagram of a radio frame for illustrating anoperation example 5.

FIG. 23 is a configuration diagram of a radio frame for illustrating theoperation example 5.

FIG. 24 is a configuration diagram of a radio frame for illustrating anoperation example 6.

FIG. 25 is a sequence diagram for illustrating the operation example 6.

FIG. 26 is a configuration diagram of a radio frame for illustrating theoperation example 6.

FIG. 27 is a configuration diagram of a radio frame for illustrating theoperation example 6.

FIG. 28 is a sequence diagram of a radio frame for illustrating anoperation example 7.

FIG. 29 is a diagram for illustrating the operation example 7.

FIG. 30 is a diagram for illustrating the operation example 7.

FIG. 31 is a sequence diagram for illustrating the operation example 7.

FIG. 32 is a configuration diagram of a radio frame for illustrating theoperation example 7.

FIG. 33 is a configuration diagram of a radio frame for illustrating theoperation example 7.

FIG. 34 is a flowchart for illustrating an operation example 8.

FIG. 35 is a flowchart for illustrating the operation example 8.

FIG. 36 is a configuration diagram of a radio frame in a mobilecommunication system according to another embodiment.

FIG. 37 is a diagram for illustrating an example usage of SA forcollision avoidance of data.

FIG. 38 is a diagram for illustrating SA period and SA regions.

FIG. 39 is a diagram for illustrating each SA determining a location ofassociated data transmissions resources.

FIG. 40 is a diagram for illustrating initial SA transmission and thesubsequent SA transmissions.

DETAILED DESCRIPTION

A first user terminal according to an embodiment, comprises: at leastone processor and at least one memory coupled to the processor. Theprocessor configured to perform processes of: determining first radioresources to be used for transmitting control information, the controlinformation indicating location of second radio resources to be used fortransmitting data by direct Device-to-Device communication; and directlytransmitting the same control information repeatedly to a second userterminal in each resource block included in the first control resources.

The processor may be configured to perform the process of randomlydetermining the first radio resources from a resource area in whichradio resources, which is able to be used for transmitting the controlinformation, is arranged.

The processor may be configured to perform a process of receivinginformation on the first radio resources from a base station.

The processor may be configured to perform the process of receiving theinformation by downlink control information from the base station.

The processor may be configured to perform the process of receiving theinformation by a Radio Resource Control (RRC) message from the basestation.

The processor may be configured to perform the process of transmittingthe information if the first user terminal exists in a cell managed bythe base station.

An apparatus for a first user terminal according to an embodimentcomprises: at least one processor and at least one memory coupled to theprocessor. The processor configured to perform processes of: determiningfirst radio resources to be used for transmitting control information,the control information indicating location of second radio resources tobe used for transmitting data by direct Device-to-Device communication;and directly transmitting the same control information repeatedly to asecond user terminal in each resource block included in the firstcontrol resources.

A mobile communication system according to an embodiment is a mobilecommunication system that supports a D2D proximity service in whichdirect communication not passing through a network is enabled, andcomprises: a first user terminal configured to decide a control resourcethat is a time-frequency resource used for transmitting controlinformation indicating a location of a data resource that is atime-frequency resource used for transmitting D2D communication data,from a control resource area having a limited range among time-frequencyresources available for the D2D proximity service, and a second userterminal configured to perform a scan of the control information withinthe control resource area.

The mobile communication system according to the embodiment comprises abase station configured to transmit control resource information fordesignating the control resource area, the control resource, or acandidate of the control resource area, to the first user terminal.

In the embodiment, the first user terminal exists in a cell managed bythe base station, and when the first user terminal does not receive thecontrol resource information from the base station, and when an unuseddata resource exists, the first user terminal transmits the controlinformation indicating the location of the unused data resource.

In the embodiment, when the first user terminal exists in a cell managedby the base station, the first user terminal transmits the controlresource information.

The mobile communication system according to the embodiment comprises athird user terminal located out of coverage, wherein when the first userterminal receives, from the third user terminal, flag informationindicating that the third user terminal is located out of coverage, thefirst user terminal transmits the control resource information to thethird user terminal.

In the embodiment, the third user terminal previously storesconfiguration information for limiting a range of the control resourcearea, and when the third user terminal receives the control resourceinformation from the first user terminal, the third user terminalprioritizes the control resource information over the configurationinformation and decides the control resource.

In the embodiment, the first user terminal previously storesconfiguration information for limiting a range of the control resourcearea, the configuration information indicates the control resource areaprovided in a first cycle, and the base station transmits, to the firstuser terminal, the control resource information for indicating thecontrol resource area provided in a second cycle that is an integralmultiple or an integral submultiple of the first cycle.

In the embodiment, by using the data resource, the first user terminaltransmits, together with the D2D communication data, the controlinformation indicating the location of a next data resource of the dataresource.

In the embodiment, the control information is arranged in an areafollowing an area in which a last D2D communication data is arrangedwithin the data resource divided into a plurality of areas.

In the embodiment, in addition to providing the control resource withinthe data resource, the first user terminal periodically provides thecontrol resource outside the data resource.

In the embodiment, when the data resource is divided into a plurality ofsmall data resources, the first user terminal transmits the same controlinformation using each of the plurality of small data resources.

In the embodiment, in the data resource, the first user terminalapplies, to the control information, a modulation and coding schemehaving an error resilience that is higher than a modulation and codingscheme applied to the D2D communication data.

In the embodiment, a plurality of types of transmission modes havingdifferent methods of improving the error resilience of controlinformation are defined, and the first user terminal selects atransmission mode to be applied to transmitting the control informationfrom among a plurality of types of transmission modes depending on anapplication used in the D2D communication.

In the embodiment, the control resource is periodically provided in atime axis direction, depending on the location of the control resourcein a previous cycle, the range of a control resource area in a nextcycle is limited, and the first user terminal decides the controlresource in the next cycle depending on the location of the controlresource in the previous cycle.

In the embodiment, before starting a decision regarding the controlresource, the first user terminal performs a scan of the controlinformation within the control resource area, and the first userterminal decides the control resource in the next cycle on a basis of anunused time-frequency resource within the scanned control resource area.

In the embodiment, a data resource area having a limited range fromamong the time-frequency resources available for the D2D proximityservice is periodically provided in a time axis direction, the range ofthe data resource area is limited depending on the location of thecontrol resource, before starting a decision regarding the controlresource, the first user terminal performs a scan of the D2Dcommunication data within the data resource area, the first userterminal assumes the time-frequency resource within the control resourcethat should indicate the location of the unused time-frequency resourceon a basis of the unused time-frequency resource within the scanned dataresource area, and the first user terminal decides the control resourcein the next cycle on a basis of the assumed time-frequency resource.

In the embodiment, when the second user terminal detects a collision ofthe control information as a result of scanning of the controlinformation, the second user terminal transmits collision informationindicating the collision of the control information, and when the firstuser terminal receives the collision information, the first userterminal thinks about a change in the location of the control resource.

In the embodiment, even when the first user terminal receives thecollision information, the first user terminal omits the thinking abouta change in the location of the control resource when the controlinformation is transmitted periodically in continuation.

In the embodiment, the first user terminal calculates a range of thecontrol resource area on a basis of a unique value of the first userterminal.

In the embodiment, together with indicating a location of the dataresource, the control information indicates a location of a controlresource indicating a location of a next data resource of the dataresource.

In the embodiment, the control resource area includes a group area and abroadcast area, in the group area, the control resource for a pluralityof user terminals configuring a D2D group are provided, and in thebroadcast area, the control resource for an unspecified user terminal isprovided.

In the embodiment, the first user terminal shares the control resourcearea dedicated to one D2D group, to which the first user terminalbelongs, with a plurality of user terminals configuring the one D2Dgroup.

In the embodiment, the first user terminal uses the control resource totransmit, together with the control information, flag informationindicating whether or not the first user terminal is located out ofcoverage.

In the embodiment, the control resource information is information fordesignating the control resource, and the base station transmits thecontrol resource information by using downlink control information.

In the embodiment, the control resource information is information fordesignating the range of the control resource, and the base stationtransmits the control resource information by using an RRC message.

A mobile communication system according to the embodiment is a mobilecommunication system that supports a D2D proximity service in whichdirect communication not passing through a network is enabled, andcomprises: a user terminal configured to decide a control resource thatis a time-frequency resource used for transmitting control informationindicating a location of a data resource that is a time-frequencyresource used for transmitting D2D communication data, fromtime-frequency resources available for the D2D proximity service, andthe user terminal uses the decided control resource repeatedly totransmit the same control information at a bit level or in units ofresource blocks.

A user terminal according to the embodiment is a user terminal used in amobile communication system that supports a D2D proximity service inwhich direct communication not passing through a network is enabled, andcomprises: a control unit configured to decide a control resource thatis a time-frequency resource used for transmitting control informationindicating a location of a data resource that is a time-frequencyresource used for transmitting D2D communication data, from a controlresource area having a limited range among time-frequency resourcesavailable for the D2D proximity service.

Embodiment

Hereinafter, the embodiment in a case where the present disclosure isapplied to a LTE system will be described.

(System Configuration)

FIG. 1 is a configuration diagram of the LTE system according to apresent embodiment.

As shown in FIG. 1, the LTE system includes a plurality of UEs (UserEquipments) 100, E-UTRAN (Evolved Universal Terrestrial Radio AccessNetwork) 10, and EPC (Evolved Packet Core) 20. The E-UTRAN 10 and theEPC 20 constitute a network.

The UE 100 is a mobile radio communication device and performs radiocommunication with a cell (a serving cell) with which a connection isestablished. The UE 100 corresponds to the user terminal.

The E-UTRAN 10 includes a plurality of eNBs 200 (evolved Node-Bs). TheeNB 200 corresponds to a base station. The eNB 200 manages a cell andperforms radio communication with the UE 100 that establishes aconnection with the cell.

It is noted that the “cell” is used as a term indicating a minimum unitof a radio communication area, and is also used as a term indicating afunction of performing radio communication with the UE 100.

The eNB 200, for example, has a radio resource management (RRM)function, a function of routing user data, and a measurement controlfunction for mobility control and scheduling.

The EPC 20 includes MME (Mobility Management Entity)/S-GW(Serving-Gateway) 300 and OAM 400 (Operation and Maintenance). Further,the EPC 20 corresponds to a core network.

The MME is a network node that performs various mobility controls andthe like, for the UE 100 and corresponds to a controller. The S-GW is anetwork node that performs control to transfer user data and correspondsto a mobile switching center.

The OAM 400 is a server device managed by an operator and performsmaintenance and monitoring of the E-UTRAN 10.

Next, configurations of the UE 100 and the eNB 200 will be described.

FIG. 2 is a block diagram of the UE 100. As shown in FIG. 2, the UE 100includes an antenna 101, a radio transceiver 110, a user interface 120,GNSS (Global Navigation Satellite System) receiver 130, a battery 140, amemory 150, and a processor 160. The memory 150 and the processor 160configure a control unit.

The UE 100 may not have the GNSS receiver 130. Furthermore, the memory150 may be integrally formed with the processor 160, and this set (thatis, a chip set) may be called a processor 160′.

The antenna 101 and the radio transceiver 110 are used to transmit andreceive a radio signal. The antenna 101 includes a plurality of antennaelements. The radio transceiver 110 converts a baseband signal outputfrom the processor 160 into the radio signal, and transmits the radiosignal from the antenna 101. Furthermore, the radio transceiver 110converts the radio signal received by the antenna 101 into the basebandsignal, and outputs the baseband signal to the processor 160.

The user interface 120 is an interface with a user carrying the UE 100,and includes, for example, a display, a microphone, a speaker, variousbuttons and the like. The user interface 120 receives an operation froma user and outputs a signal indicating the content of the operation tothe processor 160.

The GNSS receiver 130 receives a GNSS signal in order to obtain locationinformation indicating a geographical location of the UE 100, andoutputs the received signal to the processor 160.

The battery 140 accumulates a power to be supplied to each block of theUE 100.

The memory 150 stores a program to be executed by the processor 160 andinformation to be used for a process by the processor 160.

The processor 160 includes a baseband processor that performs modulationand demodulation, encoding and decoding and the like on the basebandsignal, and a CPU (Central Processing Unit) that performs variousprocesses by executing the program stored in the memory 150. Theprocessor 160 may further include a codec that performs encoding anddecoding on sound and video signals. The processor 160 executes variousprocesses and various communication protocols described later.

FIG. 3 is a block diagram of the eNB 200. As shown in FIG. 3, the eNB200 includes an antenna 201, a radio transceiver 210, a networkinterface 220, a memory 230, and a processor 240. The memory 230 and theprocessor 240 constitute a control unit. In addition, the memory 230 isintegrated with the processor 240, and this set (that is, a chipset) maybe called a processor 240′.

The antenna 201 and the radio transceiver 210 are used to transmit andreceive a radio signal. The antenna 201 includes a plurality of antennaelements. The radio transceiver 210 converts the baseband signal outputfrom the processor 240 into the radio signal, and transmits the radiosignal from the antenna 201. Furthermore, the radio transceiver 210converts the radio signal received by the antenna 201 into the basebandsignal, and outputs the baseband signal to the processor 240.

The network interface 220 is connected to the neighboring eNB 200 viathe X2 interface and is connected to the MME/S-GW 300 via the S1interface. The network interface 220 is used in communication performedon the X2 interface and communication performed on the S1 interface.

The memory 230 stores a program to be executed by the processor 240 andinformation to be used for a process by the processor 240.

The processor 240 includes the baseband processor that performsmodulation and demodulation, encoding and decoding and the like on thebaseband signal and a CPU that performs various processes by executingthe program stored in the memory 230. The processor 240 executes variousprocesses and various communication protocols described later.

FIG. 4 is a protocol stack diagram of a radio interface in the LTEsystem.

As shown in FIG. 4, the radio interface protocol is classified into alayer 1 to a layer 3 of an OSI reference model, wherein the layer 1 is aphysical (PHY) layer. The layer 2 includes MAC (Media Access Control)layer, RLC (Radio Link Control) layer, and PDCP (Packet Data ConvergenceProtocol) layer. The layer 3 includes RRC (Radio Resource Control)layer.

The PHY layer performs encoding and decoding, modulation anddemodulation, antenna mapping and demapping, and resource mapping anddemapping. The PHY layer provides a transmission service to an upperlayer by using a physical channel. Between the PHY layer of the UE 100and the PHY layer of the eNB 200, data is transmitted through thephysical channel.

The MAC layer performs priority control of data, and a retransmissionprocess and the like by hybrid ARQ (HARQ). Between the MAC layer of theUE 100 and the MAC layer of the eNB 200, data is transmitted via atransport channel. The MAC layer of the eNB 200 includes a transportformat of an uplink and a downlink (a transport block size, a modulationand coding scheme and the like) and a MAC scheduler to decide a resourceblock to be assigned.

The RLC layer transmits data to an RLC layer of a reception side byusing the functions of the MAC layer and the PHY layer. Between the RLClayer of the UE 100 and the RLC layer of the eNB 200, data istransmitted via a logical channel.

The PDCP layer performs header compression and decompression, andencryption and decryption.

The RRC layer is defined only in a control plane. Between the RRC layerof the UE 100 and the RRC layer of the eNB 200, a control signal (an RRCmessage) for various types of setting is transmitted. The RRC layercontrols the logical channel, the transport channel, and the physicalchannel in response to establishment, re-establishment, and release of aradio bearer. When an RRC connection is established between the RRC ofthe UE 100 and the RRC of the eNB 200, the UE 100 is in a connectedstate, and when the RRC connection is not established, the UE 100 is inan idle state.

NAS (Non-Access Stratum) layer positioned above the RRC layer performssession management, mobility management and the like.

FIG. 5 is a configuration diagram of a radio frame used in the LTEsystem. In the LTE system, OFDMA (Orthogonal Frequency DivisionMultiplexing Access) is employed in a downlink, and SC-FDMA (SingleCarrier Frequency Division Multiple Access) is employed in an uplink,respectively.

As shown in FIG. 5, the radio frame is configured by 10 subframesarranged in a time direction, wherein each subframe is configured by twoslots arranged in the time direction. Each subframe has a length of 1 msand each slot has a length of 0.5 ms. Each subframe includes a pluralityof resource blocks (RBs) in a frequency direction, and a plurality ofsymbols in the time direction. Each symbol is provided at a head thereofwith a guard interval called a cyclic prefix (CP). The resource blockincludes a plurality of subcarriers in the frequency direction. A radioresource unit configured by one subcarrier and one symbol is called aresource element (RE).

Among radio resources assigned to the UE 100, a frequency resource canbe designated by a resource block and a time resource can be designatedby a subframe (or slot).

In the downlink, an interval of several symbols at the head of eachsubframe is a control region mainly used as a physical downlink controlchannel (PDCCH). Furthermore, the remaining interval of each subframe isa region that can be mainly used as a physical downlink shared channel(PDSCH). Moreover, in each subframe, cell-specific reference signals(CRSs) are distributed and arranged.

In the uplink, both ends in the frequency direction of each subframe arecontrol regions mainly used as a physical uplink control channel(PUCCH). Furthermore, the center portion in the frequency direction ofeach subframe is a region that can be mainly used as a physical uplinkshared channel (PUSCH). Moreover, in each subframe, a demodulationreference signal (DMRS) and a sounding reference signal (SRS) arearranged.

(D2D Communication)

Next, description will be provided by comparing the D2D communicationwith the normal communication (the cellular communication) in the LTEsystem.

FIG. 6 is a diagram illustrating a data path in the cellularcommunication. In this case, FIG. 6 illustrates the case in which thecellular communication is performed between UE 100-1 that establishes aconnection with eNB 200-1 and UE 100-2 that establishes a connectionwith eNB 200-2. It is noted that the data path indicates a transfer pathof user data (a user plane).

As illustrated in FIG. 6, the data path of the cellular communicationpasses through the network. Specifically, the data path is set to passthrough the eNB 200-1, the S-GW 300, and the eNB 200-2.

FIG. 7 is a diagram illustrating a data path in the D2D communication.In this case, FIG. 7 illustrates the case in which the D2D communicationis performed between the UE 100-1 that establishes a connection with theeNB 200-1 and the UE 100-2 that establishes a connection with the eNB200-2.

As illustrated in FIG. 7, the data path of the D2D communication doesnot pass through the network. That is, direct radio communication isperformed between UEs. As described above, when the UE 100-2 exists inthe vicinity of the UE 100-1, the D2D communication is performed betweenthe UE 100-1 and the UE 100-2, thereby obtaining an effect that atraffic load on the network and a battery consumption amount of the UE100 are reduced, for example.

It is noted that cases in which the D2D communication is started include(a) a case in which the D2D communication is started after a proximalterminal is discovered by performing an operation for discovering aproximal terminal, and (b) a case in which the D2D communication isstarted without performing an operation for discovering a proximalterminal.

For example, in the above-described case (a), one UE 100 of the UE 100-1and the UE 100-2 discovers the other UE 100 existing in the proximity ofthe one UE 100, so that the D2D communication is started.

In such a case, in order to discover the proximal terminal, the UE 100has a (Discover) function of discovering another UE 100 existing in theproximity of the UE 100, and/or a (Discoverable) function of beingdiscovered by another UE 100.

Specifically, the UE 100-1 transmits a discovery signal (Discoverysignal/Discoverable signal) that is used to either discover a proximalterminal or to be discovered by a proximal terminal. The UE 100-2 thatreceives the discovery signal discovers the UE 100-1. When the UE 100-2transmits a response to the discovery signal, the UE 100-1 that hastransmitted the discovery signal discovers the UE 100-2, which is theproximal terminal.

It is noted that the UE 100 need not necessarily perform the D2Dcommunication even upon discovering a proximal terminal, for example,after mutually discovering each other, the UE 100-1 and the UE 100-2 mayperform a negotiation, and determine whether or not to perform the D2Dcommunication. When each of the UE 100-1 and the UE 100-2 agrees toperform the D2D communication, the D2D communication starts. It is notedthat when the UE 100-1 does not perform the D2D communication afterdiscovering a proximal terminal, the UE 100-1 may report, to an upperlayer (for example, an application), the discovery of the proximal UE100 (that is, the UE 100-2). For example, the application is capable ofexecuting a process based on the report (for example, a process ofplotting the position of the UE 100-2 in the geographical information).

Moreover, the UE 100 is capable of reporting the discovery of a proximalterminal to the eNB 200, and is also capable of receiving, from the eNB200, an instruction regarding whether to communicate with the proximalterminal through the cellular communication or through the D2Dcommunication.

On the other hand, in the above-described case (b), for example, the UE100-1 starts the transmission (such as a notification throughbroadcasting) of a signal for the D2D communication without specifying aproximal terminal. Thus, the UE 100 is capable of starting the D2Dcommunication regardless of the existence of the discovery of a proximalterminal. It is noted that the UE 100-2 that is performing the standbyoperation for the signal for the D2D communication performssynchronization or/and demodulation on the basis of the signal from theUE 100-1.

(Decision of Control Resource and Data Resource)

Next, an operation, in which the UE 100 decides a control resource and adata resource, will be described.

The UE 100 decides a control resource (a SA resource), which is atime-frequency resource used for transmitting control information (SA:Scheduling Assignment) indicating a location of the data resource, fromamong the time-frequency resources available for the D2D proximityservice.

Specifically, the UE 100 decides the SA resource from a control resourcearea (a SA resource area) having a limited range, from among thetime-frequency resources available for the D2D proximity service. The SAresource area is an area in which SA resources used to transmit SA bythe UE 100 are arranged. For example, the SA resource area isconcentrated in a predetermined range. Specifically, as shown in FIG. 8,the SA resource area may be provided periodically in a time axisdirection, or as shown in FIG. 9, the SA resource area may be providedin a predetermined frequency band. As described later, the range of theSA resource area is limited on the basis of SA resource informationtransmitted from the eNB 200 or configuration information (Pre-config)that is previously stored in the UE 100.

Moreover, the UE 100-1 decides a data resource, which is atime-frequency resource used for transmitting the D2D communicationdata, from among time-frequency resources available for a D2D proximityservice.

The UE 100 is capable of deciding the data resources from the dataresource area with a limited range in the time-frequency resourcesavailable for the D2D proximity service. The data resource area is anarea in which data resources used to transmit the D2D communication databy the UE 100 are arranged. For example, the data resource area is thearea excluding the SA resource area from the area in which thetime-frequency resources available for the D2D proximity service arearranged. As described later, the range of the data resource area may belimited on the basis of data resource information transmitted from theeNB 200 or configuration information.

The UE 100 uses the decided SA resource to transmit the SA (SA 1)indicating the locations of the decided data resources (DATAs 11 to 13).On the other hand, the other UE 100 receives the SA by scanning the SAwithin the SA resource area with a limited range. The SA allows theother UE 100 that receives the SA to grasp the locations of dataresources, which are used by the UE 100 to transmit D2D communicationdata. By scanning the locations (area) of the grasped data resources,the UE 100 is capable of receiving the D2D communication data from theUE 100-1.

It is noted that as shown in FIG. 8, the SA may directly indicate thedata resources, or as shown in FIG. 9, the SA may indicate the range ofthe data resources.

(Range of SA Resource Area)

The UE 100 limits the range of the SA resource area on the basis of SAresource information transmitted from the eNB 200 or configurationinformation (Pre-config) that is previously stored in the UE 100.

The SA resource information and the configuration information isinformation for designating an SA resource area, an SA resource, orcandidates of the SA resource area. The SA resource information may bean assignment rule for limiting the range of the SA resource area. Forexample, the SA resource information includes information indicating atleast any one of a frequency band and/or a time zone of the SA resourcearea, an offset (a time and/or a frequency), and a cycle (a time).

The offset, for example, is expressed using the following Equation.(offset)=(SFN×10+subframe)mod(cycle)

Furthermore, the SA resource information may include informationindicating at least any one of a size of one SA resource, the number ofSA resources assignable by the UE 100 (and/or the presence or absence ofthe SA resource), and a modulation and coding scheme (MCS) applied tothe SA.

For example, in FIG. 8, the SA resource information includes the timezone of the SA resource area (the assignment range of the SA), the cycleof the SA resource area, and the offset of the SA. The UE 100 limits therange of the SA resource area on the basis of the SA resourceinformation and the following Equation.((SFN×10+subframe)−(offset of SA))mod(cycle of SA resourcearea)<(assignment range of SA)

Moreover, in FIG. 9, the SA resource information is a frequency band ofthe SA resource area.

The UE 100 may decide a data resource on the basis of the data resourceinformation received from the eNB 200.

It is noted that the data resource information is information fordesignating a data resource area, a data resource, or a candidate of thedata resource area. The data resource information could also be anassignment rule for limiting the range of the data resource area. Forexample, the data resource information includes information indicatingat least any one of a frequency band and/or a time zone of the dataresource area, a cycle (a time) of the data resource area, an offset (atime and/or a frequency) from SA indicating a data resource start, and adata resource interval. The data resource information may includeinformation indicating at least any one of a resource size of one dataresource, the number of data resources, and a modulation and codingscheme (MCS) applied to D2D communication data.

The configuration information may include information having the samecontent as the data resource information. It is noted that the UE 100 iscapable of updating the configuration information on the basis of updateinformation received from the eNB 200.

Since the UE 100 scans the SA within the SA resource area with a limitedrange, it is possible to effectively scan the SAs. Moreover, since theUE 100 scans the data resources within the data resource area with alimited range, it is possible to effectively scan the data resources.

It is noted that the eNB 200 is capable of transmitting the SA resourceinformation to the UE 100 by at least one of an RRC message (forexample, SIB (System Information Block)) or DCI (Downlink ControlInformation). For example, in the case of transmitting the SA resourceinformation for (directly) designating an SA resource, the eNB 200 iscapable of transmitting the SA resource information by using DCI. On theother hand, in the case of transmitting the SA resource information for(directly) designating the range (that is, an SA resource area) of theSA resources, the eNB 200 is capable of transmitting the SA resourceinformation by using an RRC message (for example, SIB).

The eNB 200 is capable of transmitting the data resource information tothe UE 100 by at least one of an RRC message (for example, SIB) or DCI.For example, in the case of transmitting the data resource informationfor (directly) designating a data resource, the eNB 200 is capable oftransmitting the data resource information by using DCI. On the otherhand, in the case of transmitting the data resource information for(directly) designating a range (that is, a data resource area) of thedata resource, the eNB 200 is capable of transmitting the data resourceinformation by using an RRC message (for example, SIB).

(Operation Example According to the Present Embodiment)

Next, an operation example according to the present embodiment will bedescribed. It is noted that a description will be provided whilefocusing on a portion different from the other operation examples, and adescription of a similar portion will be appropriately omitted.

(A) Operation Example 1

An operation example 1 will be described using FIG. 10. FIG. 10 is aconfiguration diagram of a radio frame for illustrating the operationexample 1.

The operation example 1 is a case in which the range of an SA resourcein this cycle is limited depending on the locations of SA resources in aprevious cycle.

As shown in FIG. 10, the SA resource area is periodically provided in atime axis direction.

When the UE 100 wants to transmit the D2D communication data, the UE 100performs a scan within the SA resource area before starting the decisionregarding the SA resources. Next, the UE 100 decides the SA resources inthe next cycle depending on the locations of the SA resources in aprevious cycle. Specifically, the UE 100 decides the SA resources in thenext cycle on the basis of the unused SA resources within the scanned SAresource area.

Specifically, as shown in FIG. 10, the UE 100 receives SA 11 and SA 21by scanning the SA resource area. The UE 100 decides, as SA resources,the resources at the locations of (subframe 11, RB 3-4) by avoiding thelocations of the SA 11 and the SA 21. The UE 100 uses the decided SAresources to transmit SA 31.

According to the operation example 1, since the UE 100 is capable ofgrasping the locations of the next SAs of another UE 100 when the otherUE 100 is continuously transmitting SAs, it is possible to effectivelyscan the SAs. In addition, since the UE 100 is capable of deciding theSA resources by avoiding the locations of the SAs of the other UE 100,it is possible to avoid the collision of SAs.

It is noted that as shown in FIG. 10, the range of the data resourcearea may be limited depending on the locations of the SAs. Specifically,the range of the data resource area is limited so that the locations ofthe SAs and the location of the data are in the same frequency band.

(B) Modification of Operation Example 1

Next, a modification of the operation example 1 will be described byusing FIG. 11. FIG. 11 is a configuration diagram of a radio frame forillustrating a modification of the operation example 1.

In the operation example 1, the UE 100 scans the SA resource area, butin the modification of the operation example 1, the UE 100 scans thedata resource area.

As shown in FIG. 11, the SA resource area is periodically provided in atime axis direction. As a result, the data resource area is partitionedinto SA resource areas and periodically provided in a time axisdirection.

Moreover, in addition to the fact that the range of the SA resources ina next cycle is limited depending on the locations of SA resources in aprevious cycle, the range of the data resource area is limited dependingon the locations of the SA resources.

When the UE 100 wants to transmit the D2D communication data, the UE 100performs a scan within the data resource area before starting thedecision regarding the SA resources. Next, the UE 100 presumes the SAresources that should indicate the unused data resources on the basis ofthe unused data resources within the scanned data resource area. The UE100 uses the fact that the range of a data resource is limited dependingon a location of an SA resource to assume the SA resources. The UE 100decides the SA resources in the next cycle on the basis of the assumedSA resources.

Specifically, as shown in FIG. 11, the UE 100 grasps the fact that thedata resource at the location of (subframe 8) is an unused data resourcebased on the scanning of the data resource area (subframes 3-10). The UE100 assumes the SA resources that should indicate the unused dataresources on the basis of the configuration information or the like. Onthe basis of the configuration information or the like, the UE 100assumes that the SA 11 is the SA that should indicate the location ofthe unused data resources. The UE 100 assumes that the SA resource atthe location corresponding to the location of the SA 11 in the nextcycle (subframe 11) is not used. Thus, the UE 100 transmits the SA 31using the SA resource at the location (subframe 11, RB 2-3).

It is noted that rather than scanning the entire data resource area, theUE 100 may scan only the area of a subframe 8-9 from where the last D2Dcommunication data is transmitted. Alternatively, when the number ofdata resources indicated by SA is less than the maximum number of thetransmitted D2D communication data on the basis of the configurationinformation or the like, the UE 100 may decide the SA resources in thenext cycle depending on the location of the SA resources used fortransmitting the SA.

According to the modification of the operation example 1, similarly tothe operation example 1, since it is possible to grasp the locations ofthe next SAs of another UE 100, it is possible to effectively scan theSAs. Moreover, it is possible to avoid the collision of SAs.

(C) Operation Example 2

An operation example 2 will be described. In the operation example 2,the UE 100 calculates the range of the SA resource area on the basis ofa unique value of the UE 100.

For example, the UE 100 decides the range of the SA resource area (theSA resources) by the following Equation, on the basis of a randomnumber, a UE-unique value, and the number of SA resources.Range of SA resource area=(Rand(UE−unique value))mod number of SAresources

The UE-unique value, for example, is a manufacturing number or atelephone number, etc.

The UE 100 decides the SA resources on the basis of the calculated rangeof the SA resource area.

Moreover, the UE 100 may decide the range of the SA resource area by thefollowing Equation.Range of SA resource area=(Rand(UE−unique value×time))mod number of SAresources

The time, for example, is the time point of calculating the range of theSA resource area.

According to the operation example 2, since the SA resources areselected randomly, it is possible to prevent the SA resources from beingunevenly selected. As a result, it is possible to avoid the collision ofSAs.

(D) Operation Example 3

An operation example 3 will be described using FIG. 12. FIG. 12 is aconfiguration diagram of a radio frame for illustrating the operationexample 3.

In the operation example 3, along with indicating a location of the dataresources in the same cycle, the SA indicates a location of an SAresource indicating the location of the next data resources.

The UE 100 decides the location of a data resource, and the location ofan SA resource indicating the location of the data resource. The UE 100further decides the location of an SA resource in a next cycle. The UE100 uses the decided SA resource to transmit the location of the decideddata resource, and the SA indicating the location of the SA resource inthe next cycle.

For example, as shown in FIG. 12, the UE 100-1 transmits the SA 11 thatindicates the location of data resources DATA 11 to DATA 13, and alsoindicates the location of a SA resource SA 12.

Here, it is assumed that the possibility of assigning three DATAs aftertwo [subframes] in cycles of two [subframes] for the SA is defined inthe configuration information or the like.

The UE 100-2 understands the location of the data resources (DATAs 11 to13) used by the UE 100-1 that transmits the SA 11, on the basis of theSA 11. The UE 100-2 decides the SA 21 on the basis of the location ofthe data resources indicated by the SA 11.

It is noted that the UE 100-2, for example, may transmit the SA 21 usingonly the SA resource at the location (subframe 4, RB 2). In such a case,since the size of the SA is different from the size of the D2Dcommunication data, the SA 21 may include information indicating thatthe size of the D2D communication data extends in a frequency directionfrom the size of the SA.

According to the operation example 3, since the reservation of the nextSA resource is possible, the UE 100 is capable of deciding the SAresources by avoiding the location of the reserved SA resource. As aresult, it is possible to avoid the collision of SAs.

(E) Operation Example 4

An operation example 4 will be described using FIG. 13 to FIG. 15. FIG.13 to FIG. 15 are configuration diagrams of a radio frame forillustrating the operation example 4.

In the operation example 4, the UE 100 uses the data resources totransmit the SA indicating the location of the data resources in thenext cycle along with the D2D communication data.

Specifically, as shown in FIG. 13, the UE 100 uses the SA resource totransmit SA 10 indicating the location of the data resources (the rangeof the data resources). Thereafter, the UE 100 uses the data resourcesto transmit the DATA 11, the DATA 12, and SA 20.

Moreover, the UE 100 transmits the SA 20 immediately after the last DATA12 using the data resources. The SA 20 is transmitted using the lastdata resource of a series of data resources indicated by the SA 10. Inother words, the SA 20 is arranged in an area following the area inwhich the last DATA 12 is arranged (the last resource block of the lastdata resource) among the data resources divided in a plurality of areas(the area of the DATA 11, the area of the DATA 12, and the area of theSA 20). Therefore, it is possible to acquire the SA after the series ofD2D communication data has been received.

The location of the SA 20 may be a predetermined location (for example,the last resource block of the last data resource). Alternatively, theUE 100 may dynamically set the location of the SA 20, and transmit theSA 10 indicating the location of the data resources and the location ofthe SA 20.

As shown in FIG. 14, the UE 100 may indicate that when endingtransmitting the D2D communication data, transmitting the D2Dcommunication data is ended by not transmitting the SA using dataresources.

Alternatively, as shown in FIG. 15, the UE 100 may transmit SA 30indicating information (no assignment) that indicates the termination oftransmitting the D2D communication data using data resources.

According to the operation example 4, since another UE 100 is capable ofreceiving the SA by scanning the data resources indicated by the SA, itis possible to effectively scan the SAs.

(F) Modification 1 of Operation Example 4

Next, a modification 1 of the operation example 4 will be described byusing FIG. 16 to FIG. 18. FIG. 16 and FIG. 17 are configuration diagramsof a radio frame for illustrating the modification 1 of the operationexample 4. FIG. 18 is a diagram for illustrating SIB according to themodification 1 of the operation example 4.

In the modification 1 of the operation example 4, in addition toproviding an SA resource within a data resource, the UE 100 periodicallyprovides an SA resource outside the data resource.

For example, as shown in FIG. 16, the UE 100 transmits the SA in whichthe SA resource that is outside the data resource is used, in a cycle(12 [subframes] cycle) that is longer than the transmission cycle of theseries of D2D communication data. Alternatively, as shown in FIG. 17,the UE 100 transmits the SA in which the SA resource that is outside thedata resource is used, in a cycle (six [subframes] cycle) that is sameas the transmission cycle of the series of D2D communication data.

The UE 100 may decide, on the basis of a UE identifier (such as C-RNTI),the transmission cycle (transmission interval) of the SA in which the SAresource is used. The UE identifier, for example, is C-RNTI, a part ofC-RNTI (for example, the last two digits), or a predetermined anddedicated identifier (such as Public-Safety dedicated ID).

Specifically, the UE 100 may be decided using the following Equation.Transmission interval=(UE identifier)mod(configuration value)×n

The UE 100 may set the configuration value and n on the basis of theconfiguration information, or the UE 100 may set the configuration valueand n on the basis of a candidate of the configuration value received bySIB (see FIG. 18). Moreover, the UE 100 may use a value that is set in afixed manner in SIM, etc. to set the configuration value and n.Alternatively, the UE 100 may set the configuration value and ndepending on the application that is used in the D2D communication.

Moreover, as a transmission mode applied to transmitting SA, the UE 100is capable of selecting the transmission mode of the operation example 4or the transmission mode of the modification 1 of the operation example4, for example, depending on the application used in the D2Dcommunication. Specifically, when the application used in the D2Dcommunication is an application for real-time communication ormission-critical communication (such as an emergency call or a preferredcall), the UE 100 selects the transmission mode of the modification 1 ofthe operation example 4; otherwise the UE 100 selects the transmissionmode of the operation example 4.

According to the modification 1 of the operation example 4, since aplurality of SAs indicating the location of the same data resource aretransmitted, the UE 100 need not scan an SA that is transmitted using anSA resource as long as it is possible to receive SAs transmitted using adata resource. Therefore, it is possible to effectively scan the SAs.Moreover, even in the case of failure in receiving an SA transmittedusing a data resource, it is possible to more accurately receive the D2Dcommunication data by performing a scan of the SAs transmitted using anSA resource.

(G) Modification 2 of Operation Example 4

A modification 2 of the operation example 4 will be described by usingFIG. 19. FIG. 19 is a configuration diagram of a radio frame forillustrating the modification 2 of the operation example 4.

In the modification 2 of the operation example 4, when a data resourceis divided into a plurality of small data resources, the UE 100transmits the same SA (with the same contents) using each of theplurality of small data resources.

For example, as shown in FIG. 19, the data resource indicated by the SA10 is divided into a data resource used for transmitting the DATA 11,and a data resource used for transmitting the DATA 12. The UE 100 usesthe plurality of small data resources to transmit the SA 22 accompaniedby the DATA 11, and the SA 20 accompanied by the DATA 12. Each of the SA22 and the SA 20 indicate the location of the next data resources.

Similarly, each of the plurality of SAs (SA 32, SA 33, SA 34, and the SA30) transmitted using the next data resources indicates the location ofthe further next data resources.

It is noted that rather than accompanying each of the plurality of SAsat the end of DATA, the UE 100 may accompany the DATA to each of theplurality of SAs. It is noted that the same is applicable in anotheroperation example as well.

Moreover, as a transmission mode applied to transmitting SA, the UE 100is capable of selecting the transmission mode of the operation example 4or the transmission mode of the modification 2 of the operation example4, for example, depending on the application used in the D2Dcommunication. Specifically, when the application used in the D2Dcommunication is an application for a file transfer, the UE 100 selectsthe transmission mode of the modification 2 of the operation example 4;otherwise the UE 100 selects the transmission mode of the operationexample 4.

According to the modification 2 of the operation example 4, it ispossible to more accurately receive the SAs as compared to the operationexample 1.

(H) Modification 3 of Operation Example 4

A modification 3 of the operation example 4 will be described by usingFIG. 20. FIG. 20 is a configuration diagram of a radio frame forillustrating the modification 3 of the operation example 4.

In the modification 3 of the operation example 4, in a data resource,the UE 100 applies, to the SAs, MCS (modulation and coding scheme)having an error resilience that is higher than MCS applied to the D2Dcommunication data.

For example, in the operation example 4, the UE 100 applies 16QAM to theDATA and the SA transmitted using the data resource indicated by the SA.In contrast, in the modification of the operation example 4, as shown inFIG. 20, the UE 100 applies 16QAM to the DATA (the DATA 11 and the DATA12) transmitted using the data resource indicated by the SA 10, andapplies BPSK, which has a higher error resilience than 16QAM, to the SA20 transmitted using the data resource indicated by the SA 10.

Moreover, as a transmission mode applied to transmitting SA, the UE 100is capable of selecting the transmission mode of the operation example 4or the transmission mode of the modification 3 of the operation example4, for example, depending on the application used in the D2Dcommunication. Specifically, when the application used in the D2Dcommunication is an application for a file transfer, the UE 100 selectsthe transmission mode of the modification 3 of the operation example 4;otherwise the UE 100 selects the transmission mode of the operationexample 4.

According to the modification 2 of the operation example 4, it ispossible to more accurately receive the SAs as compared to the operationexample 1.

(I) Modification 4 of Operation Example 4

A modification 4 of the operation example 4 will be described by usingFIG. 21. FIG. 21 is a flowchart for illustrating the modification 4 ofthe operation example 4.

In the modification 4 of the operation example 4, a plurality of typesof transmission modes having different methods of improving the errorresilience of SA are defined. The UE 100 selects a transmission mode tobe applied to transmitting SAs from among a plurality of types oftransmission modes depending on the application used in the D2Dcommunication.

As shown in FIG. 21, in step S101, before starting transmitting the SA,the UE 100 determines whether the application used in the D2Dcommunication is an application for real-time communication (ormission-critical communication). When the application is an applicationfor the real-time communication, the UE 100 executes the process of stepS102; otherwise the UE 100 executes the process of step S103.

In step S102, the UE 100 selects the transmission mode by which an SAresource is periodically provided outside the data resource (themodification 1 of the operation example 4).

In step S103, the UE 100 determines whether the application used in theD2D communication is an application for a file transfer. When theapplication is an application for a file transfer, the UE 100 executesthe process of step S104; otherwise the UE 100 executes the process ofstep S105.

In step S104, the UE 100 selects the transmission mode for transmittingthe same SA using each of a plurality of small data resources (themodification 2 of the operation example 4), and the transmission modefor applying MCS with a high error resilience to the SA (themodification 3 of the operation example 4).

In step S105, the UE 100 selects the transmission mode in which theerror resilience of the SA is normal (the operation example 4).

According to the modification 4 of the operation example 4, the UE 100is capable of selecting a transmission mode in which the errorresilience of the SA is appropriate depending on the application used inthe D2D communication.

(J) Operation Example 5

An operation example 5 will be described using FIG. 22 and FIG. 23. FIG.22 and FIG. 23 are configuration diagrams of a radio frame forillustrating the operation example 5.

In the operation example 5, an SA resource area for a D2D group isprovided.

As shown in FIG. 22, the SA resource area includes an SA resource areafor a D2D group (a D2D group area) and an SA resource area for broadcast(a broadcast area).

In the D2D group area, an SA resource for a plurality of UEs 100configuring a D2D group are provided. In the broadcast area, an SAresource for an unspecified UE 100 is provided.

As shown in FIG. 22, the D2D group area and the broadcast area may beseparated in a frequency direction. Alternatively, as shown in FIG. 23,the D2D group area and the broadcast area may be separated in a timeaxis direction. Specifically, the D2D group area and the broadcast areamay be separated for each frame.

As shown in FIG. 22, when transmitting SA to the UEs 100 configuring theD2D group, the UE 100 transmits the SA using the SA resource within theD2D group area. On the other hand, when transmitting SA to anunspecified UE 100, the UE 100 transmits the SA using the SA resourcewithin the broadcast area.

Moreover, the UE 100 shares an SA resource area (the SA resources of theSA 11 and the SA 12) dedicated to a D2D group 1, to which the UE 100belongs, with the plurality of UEs 100 configuring the D2D group 1.Other plurality of UEs 100 configuring another D2D group 2 shares the SAresource area (the SA resources of the SA 21 and the SA 22) dedicated tothe D2D group 2. In other words, the UEs 100 belonging to the D2D group1 are prohibited from using the SA resources of the other D2D group 2.Thus, due to the assignment of a dedicated SA resource area to each ofthe D2D groups, it is possible to avoid the collision of SAs bydifferent D2D groups. In addition, as shown in FIG. 22, the SA resourcearea dedicated to the D2D group is provided at a corresponding locationin a next cycle.

In order to avoid a collision of the SAs within the D2D group 1, the UE100 transmits SA after detecting the end of a transmission of the D2Dcommunication data of another UE 100 belonging to the D2D group 1. Wheninformation indicating that transmitting the D2D communication data isended (temporarily) is included in the SA or the D2D communication data,the UE 100, for example, transmits the SA using the SA resourcededicated to the D2D group 1. It is needless to say that another methoddescribed herein may also be used.

According to the operation example 5, since the SA resource areaincludes the D2D group area and the broadcast area, the UE 100 iscapable of selecting the SA resource area to be scanned depending onwhether the partner terminal of the D2D communication is the UE 100belonging to the D2D group. As a result, it is possible to effectivelyscan the SAs.

Moreover, the UE 100 shares the SA resource area dedicated to the D2Dgroup 1, to which the UE 100 belongs, with the plurality of UEs 100configuring the D2D group 1. As a result, it is possible to moreeffectively perform scanning of the SAs because the UEs 100 belonging tothe D2D group 1 may scan only the SA resources being shared.

(K) Operation Example 6

An operation example 6 will be described using FIG. 24 and FIG. 25. FIG.24 is a configuration diagram of a radio frame for illustrating theoperation example 6. FIG. 25 is a sequence diagram for illustrating theoperation example 6.

In the operation example 6, when the UE 100-2 detects a collision of SAsas a result of scanning of the SAs, the UE 100-2 transmits collisioninformation indicating a collision of SAs. On receiving the collisioninformation, each of the UE 100-1 and the UE 100-2 examines a change inthe location of the SA resources.

It is noted that the explanation is proceeded with assuming that each UE100 is synchronized. Moreover, the explanation is proceeded withassuming that an SA resource area is provided periodically in the timeaxis, and the configuration information or the like defines that as aprinciple, each UE 100 that transmits the SA should transmit the SA byperiodically using the SA resource at the same location.

As shown in FIG. 24 and FIG. 25, in step S201, each of the UE 100-1 andUE 100-3 transmits the SA 11 and the SA 31 using the same SA resources(subframes 1 and 2).

In step S202, upon detecting a collision of SA 11, the UE 100-2transmits collision information (Collide 11). Regardless of the factthat the UE 100-2 detects a received power as a result of scanning ofthe SA resources, when an interpretation of the SA 11 fails, the UE100-2 determines that a collision of SAs is detected.

Each of the UE 100-1 and the UE 100-3 that transmits the SAs monitors(scans) the time-frequency resource using which the collisioninformation is transmitted. Each of the UE 100-1 and the UE 100-3receives the collision information as a result of scanning.

In step S203, each of the UE 100-1 and the UE 100-3 aborts transmittingthe D2D communication data (the DATAs 11 to 13, and DATAs 31 to 33).

In step S204, each of the UE 100-1 and the UE 100-3 thinks about achange in the location of the SA resources. For example, each of the UE100-1 and the UE 100-3 determines whether to change the location of theSA resource (for example, the frequency band) on the basis of a randomvalue.

The explanation is proceeded based on the fact that the UE 100-1determines that the location of the SA resource is not changed, and theUE 100-3 determines that the location of the SA resource is changed. Itis noted that the UE 100-3 decides the location (subframe 13, RB 3) asthe SA resource.

In step S205, the UE 100-1 transmits the SA 12 indicating the locationof the data resource of DATAs 14 to 16. The UE 100-2 receives the SA 12.

In step S206, the UE 100-3 transmits the SA 32 indicating the locationof the data resource of DATAs 34 to 36. The UE 100-2 receives the SA 32.

According to the operation example 6, since the UE 100-1 and the UE100-3 is capable of knowing a collision of SAs, it is possible to reducethe continuous collision of SAs.

(L) Modification of Operation Example 6

A modification of the operation example 6 will be described by usingFIG. 26 and FIG. 27. FIG. 26 and FIG. 27 are configuration diagrams of aradio frame for illustrating the operation example 6.

In the modification of the operation example 6, even when the UE 100-2that transmits the SA receives collision information, the thinking abouta change in the location of the SA resource is omitted when the SA istransmitted periodically in continuation.

As shown in FIG. 26, the explanation is proceeded with assuming that theprovision of a collision resource area in which a time-frequencyresource (a collision resource) used for transmitting collisioninformation is provided adjacent to the SA resource area is stipulatedin the configuration information or the like. Moreover, the collisionresource area is shared in transmitting collision information to thefirst [subframe] and the second [subframe] of the SA resource area.

The UE 100-1 transmits the SA 11 and the UE 100-2 transmits the SA 12.FIG. 26 is a case when there is no collision of SAs.

Next, as shown in FIG. 27, collision information (Collide 11) istransmitted using a collision resource within the collision resourcearea from the UE 100-3. Each of the UE 100-1 and the UE 100-2 receivesthe collision information.

Here, when the UE 100-1 is the UE that starts transmitting the SA, theUE 100-1 determines that the possibility of collision of the SAs of theUE 100-1 itself is high, and thus aborts transmitting the D2Dcommunication data. The UE 100-1 thinks about a change in the locationof the SA resource.

On the other hand, when the UE 100-2 periodically transmits the SA incontinuation, the UE 100-2 determines that the possibility of collisionof the SAs of the UE 00-2 itself is low, and thus does not aborttransmitting the D2D communication data. Thereafter, the UE 100-2 omitsthe thinking about a change in the location of the SA resource.

Alternatively, in order to identify which SAs of the first [subframe] orthose of the second [subframe] in the SA resource area have collided,the UE 100-3 uses a separable signal array to transmit the collisioninformation. Alternatively, in order to identify which SAs of the first[subframe] or those of the second [subframe] in the SA resource areahave collided, the UE 100-3 uses a collision resource in a slot unitcorresponding to each of the first [subframe] and the second [subframe]to transmit the collision information.

According to the modification of the operation example 6, it becomespossible to grasp a SA resource which is used to transmit SAs when acollision of the SAs occurs.

(M) Operation Example 7

An operation example 7 will be described using FIG. 28 to FIG. 32. FIG.28 is a sequence diagram for illustrating the operation example 7. FIG.29 and FIG. 30 are diagrams for illustrating the operation example 7.FIG. 31 is a sequence diagram for illustrating the operation example 7.FIG. 32 is a configuration diagram of a radio frame for illustrating theoperation example 7.

In the operation example 7, the proper use of the SA resourceinformation and the configuration information is explained.Specifically, depending on whether or not the UE 100 exists in a cellmanaged by the eNB 200, the UE 100 switches the resource information andthe configuration information, and decides the SA resource and the dataresource. Here, the resource information is at least any one of the SAresource information and the data resource information. The details areexplained below.

As illustrated in FIG. 28, in step S301, the eNB 200 broadcasts apredetermined radio signal. The predetermined radio signal is asynchronization signal (PSS: Primary Synchronization Signal/SSS:Secondary Synchronization Signal) or a cell reference signal (CRS: CellReference Signal), for example. The UE 100 receives a predeterminedradio signal from the eNB 200.

In step S302, the UE 100 attempts decoding of the predetermined radiosignal from the eNB 200. When the UE 100 fails to decode the radiosignal (in the case of “Yes”), the process of step S303 is executed. Onthe other hand, when the UE 100 is successful in decoding the radiosignal (in the case of “No”), the process of step S304 is executed.

In step S303, the UE 100 determines to be located out of coverage. It isnoted that the UE 100 determines to be located out of coverage also whenit is not possible to receive the radio signals from all eNBs 200 (thatis, the reception level of the radio signals from all eNBs 200 is belowa threshold value).

In step S304, in order to decide the SA resources and data resources onthe basis of the configuration information, the UE 100 performsPre-configure setting. In this way, when it is not possible to receivethe resource information from the eNB 200, the UE 100 is capable ofappropriately deciding the SA resources and the data resources.Thereafter, the UE 100 decides the SA resources and data resources onthe basis of the configuration information (the Pre-configure setting).

In step S305, the UE 100 uses the decided SA resource to transmit theSAs. The UE 100 may use the SA resources to transmit, together with theSAs, flag information indicating whether the UE 100 is located out ofcoverage. For example, the flag information indicates “1” when the UE100 is located in coverage (in the case of In Coverage), and indicates“0” when the UE 100 is located out of coverage (in the case of Out ofCoverage). Here, since the UE 100 is located out of coverage, the flaginformation indicates positioning out of coverage.

On the other hand, in step S306, the UE 100 determines that the UE 100exists in a cell of the eNB 200 to which transmits a predetermined radiosignal.

In step S307, the eNB 200 transmits resource information (specifically,the SA resource information) to the UE 100. The UE 100 receives theresource information.

In step S308, in order to decide the SA resources and data resources onthe basis of the resource information received from the eNB 200, the UE100 sets the configuration value indicated by the SA resourceinformation received from the eNB 200. Thereafter, the UE 100 decidesthe SA resources and data resources on the basis of the SA resource (theconfiguration value). Thereafter, the UE 100 performs the process ofstep S305.

It is noted that the UE 100 may transmit, together with the SAs, flaginformation indicating that the UE 100 is not located out of coverage.

Moreover, when a cycle of the SA resource area (a transmissionopportunity of the SA) is set periodically, the eNB 200 may set theconfiguration value of the eNB 200 to an integral multiple or in anintegral submultiple of the cycle of the SA resource area (thetransmission opportunity of the SA) in the configuration information. Inother words, when the configuration information indicates that a cycleof the SA resource area is the first cycle, the eNB 200 sets the SAresource information indicating the SA resource area provided in thesecond cycle, which is an integral multiple or an integral submultipleof the first cycle.

For example, as shown in FIG. 29, the eNB 200 transmits the SA resourceinformation of a predetermined cycle through SIB. Moreover, as shown inFIG. 30, the eNB 200 selects, as the (update information of the)configuration information, an integral multiple or an integralsubmultiple of a predetermined cycle included in the SA resourceinformation. The eNB 200 transmits the (update information of the)configuration information indicating the SA resource information of theselected cycle, to the UE 100.

As a result, the UE located out of coverage (OoC-UE) and the UE locatedin coverage of a cell (InC UE) is capable of gaining an opportunity ofreceiving D2D communication data without changing an operation oftransmitting/receiving the SAs.

Specifically, as shown in FIG. 31 and FIG. 32, in step S401, the eNB 200transmits a predetermined radio signal (PSS/SSS/CRS).

In step S402, the UE located within coverage (the InC-UE) synchronizeswith the eNB 200 on the basis of the predetermined radio signal.

In step S403, the InC-UE transmits a synchronization signal (D2DSS) forthe D2D communication.

In step S404, the UE located out of coverage (the OoC-UE) synchronizeswith the InC-UE on the basis of the D2DSS signal.

In step S405, the eNB 200 transmits the SA resource information to theInC-UE.

In step S406, the InC-UE sets the configuration value indicated by theSA resource information (the eNB 200). Specifically, the InC-UE sets thecycle of the SA resource area to two [subframes].

In step S407, the OoC-UE sets the configuration value indicated by theconfiguration information. Specifically, the OoC-UE sets the cycle ofthe SA resource area to eight [subframes].

In step S408, the InC-UE transmits the SA 1, SA 2, SA 3, SA 4 b, SA 5 b,SA 6, and SA 7 in a cycle of two [subframes] (see FIG. 32). On the otherhand, since the cycle of the SA resource area is eight [subframes], theOoC-UE is capable of receiving (decoding) the SA 3 and the SA 7.Moreover, the OoC-UE is capable of receiving (decoding) DATA 3 and theSA 4 on the basis of the data resource indicated by the SA 3. Moreover,the OoC-UE is capable of acquiring DATA 7 on the basis of the dataresource indicated by the SA 7.

FIG. 31 show a case where the OoC-UE fails the reception based on thedata resource indicated by the SA 4 and has not acquired DATA 4 and theSA 5. An OoC-UE having not acquired the SA 5 is not able to receive DATA5.

According to the operation example 7, the UE located out of coverage andthe UE located in coverage of a cell is capable of gaining anopportunity of receiving D2D communication data without changing anoperation of transmitting/receiving the SAs.

(N) Modification of Operation Example 7

A modification of the operation example 7 will be described by usingFIG. 33. FIG. 33 is a configuration diagram of a radio frame forillustrating the operation example 7.

In the modification of the operation example 7, when the UE 100 existingin a cell managed by the eNB 200 does not receive the SA resourceinformation from the eNB 200, the UE 100 decides an SA resource.

As shown in FIG. 33, the available SA resources are provided in a firstSA resource area on the basis of the SA resource information designatingthe SA resource from the eNB 200. In a second SA resource area, SAresources available in the UE 100 for which an SA resource is notdesignated from the eNB 200 are provided. Specifically, when SA resourceinformation designating SA resources from the eNB 200 is nottransmitted, and an unused data resource exists, the UE 100 uses the SAresources within the second SA resource area in order to use the unuseddata resource.

Specifically, as shown in FIG. 33, the UE 100-1, on the basis of the SAresource information from the eNB 200, uses the SA resources within thefirst SA resource area to transmit the SA 11. Moreover, the UE 100-1uses the data resources indicated by the SA 11 to transmit the DATAs 11to 13. Similarly, the UE 100-2, on the basis of the SA resourceinformation from the eNB 200, uses the SA resources within the first SAresource area to transmit the SA 21. Moreover, the UE 100-2 uses thedata resources indicated by the SA 21 to transmit the DATAs 11 to 23. Inthe next cycle, the UE 100-1 similarly transmits the SA 12. On the otherhand, the UE 100-2 does not transmit the SA.

Due to the occurrence of an unused SA resource within the SA resourcearea as a result of scanning of the SA resource area, the UE 100-3determines that an unused data resource exists. The UE 100-3 uses an SAresource within the second SA resource area to transmit the SA 31. TheUE 100-3 infers the location (subframes 15, 17, and 19) of the dataresources in the next cycle corresponding to the location (subframes 5,7, and 9) of the data resources indicated by the SA 21 in the previouscycle as the location of the unused data resources. The UE 100-3 usesthe inferred unused data resources to transmit the DATAs 31 to 33.

According to the modification of the operation example 7, it is possibleto effectively utilize the time-frequency resource.

(O) Operation Example 8

An operation example 8 will be described using FIG. 34 and FIG. 35. FIG.34 and FIG. 35 are flowcharts for illustrating the operation example 8.Specifically, FIG. 34 is a flowchart for illustrating an operation ofthe UE 100 located in coverage. FIG. 35 is a flowchart for illustratingan operation of the UE 100 located out of coverage.

In the operation example 8, an operation of the UE 100 located incoverage, and an operation of the UE 100 located out of coverage will bedescribed.

(1) Operation of UE 100 Located in Coverage Area

An operation of the UE 100 located in coverage will be described usingFIG. 34.

As shown in FIG. 34, in step S501, the UE 100 scans the SA resourcearea. Specifically, the UE 100 scans the SA resource area having alimited range on the basis of the SA resource information. The UE 100uses an SA resource within the SA resource area to receive thetransmitted SA.

Upon receiving flag information along with the received SA, the UE 100determines whether or not the flag information indicates that the otherUE 100 at the transmission source of the flag information is out ofcoverage. When the flag information indicates that the other UE 100 isout of coverage, the UE 100 executes the process of step S502. On theother hand, when the flag information indicates that the other UE 100 isnot out of coverage, the UE 100 ends the process. It is noted that whenthe UE 100 receives a plurality of instances of flag information, the UE100 ends the process only when each of the plurality of instances of theflag information indicates that the other UE 100 is not out of coverage.When any of the plurality of instances of the flag information indicatesthat the other UE 100 is out of coverage, the UE 100 executes theprocess of step S502.

In step S502, the UE 100 determines whether or not the UE 100 itselfexists in a cell. The UE 100, for example, executes the process of fromthe above-described step S402 to S404, and determines whether or not theUE 100 itself exists in the cell.

When the UE 100 itself exists in a cell, the UE 100 executes the processof step S503. When the UE 100 itself does not exist in a cell (that is,the UE 100 is located out of coverage), the UE 100 ends the process.

In step S503, the UE 100 transmits, to the other UE 100, the resourceinformation (the control resource information and/or the data resourceinformation) received from the cell in which the UE 100 exists. The UE100 may notify the resource information through broadcast, or maytransmit the resource information to the UE 100 located out of coveragethrough unicast. Moreover, the UE 100 may use an SA resource to transmitthe resource information, or may use a data resource to transmit theresource information.

The UE 100 may transmit, together with the resource information, flaginformation indicating that the UE 100 is not located out of coverage.

As a result, the other UE 100 located out of coverage is capable ofreceiving the resource information. The other UE 100 that receives theresource information is capable of performing the operation describedbelow.

(2) Operation of UE 100 Located Out of Coverage

Next, an operation of the UE 100 (the UE 100-2) located out of coveragewill be described using FIG. 35.

The explanation is proceeded with assuming that when the UE 100-2 islocated out of coverage, the UE 100-2 receives the resource informationfrom the UE 100-1 existing in a cell.

As shown in FIG. 35, in step S601, the UE 100-2 decides the SA resourcesand data resources. The UE 100-2 decides the SA resources and the dataresources by prioritizing the resource information (the SA resourceinformation and the data resource information) over the configurationinformation.

It is noted that when the contents of the data resource information aremore recent than the contents of the updated configuration information,the UE 100-2 may decide the SA resources and the data resources on thebasis of the configuration information. The UE 100-2 may decide the SAresources and the data resources on the basis of the resourceinformation received from the UE 100-1.

In step S602, when the UE 100-2 determines that there is a risk ofcollision of SA transmitted using the SA resource decided in step S601and SA and/or the D2D communication data transmitted by the UE 100existing in a cell (in the case of “Yes”), the UE 100-2 executes theprocess of step S603, and when the UE 100-2 determines that there is norisk of collision (in the case of “No”), the UE 100-2 executes theprocess of step S604.

Moreover, when the UE 100-2 determines that there is a risk of collisionof the D2D communication data transmitted using the data resourcedecided in step S601 with SA and/or the D2D communication datatransmitted by the UE 100 existing in a cell (in the case of “Yes”), theUE 100-2 executes the process of step S603, and when the UE 100-2determines that there is no risk of the collision (in the case of “No”),the UE 100-2 executes the process of step S604.

For example, the UE 100-2 performs a scan of the SA resources within theresource area having a limited range on the basis of the resourceinformation from the UE 100-1 existing in a cell. The UE 100-2 graspsthe SA resources used for transmitting the SA, and infers the SAresources used for transmitting the SA on the basis of the resourceinformation. Moreover, the UE 100-2 grasps the data resources indicatedby the received SA.

The UE 100-2 determines whether the inferred SA resources and thegrasped data resources (the resources of the UE 100 located in coverage)do nor overlap the SA resources and the data resources that the UE 100-2uses for transmission (the resources of the UE 100-2 itself). When theUE 100-2 determines that the resources of the UE 100 located in coverageoverlap the resources of the UE 100-2 itself, the UE 100-2 determinesthat there is a risk of a collision, and when the UE 100-2 determinesthat the resources of the UE 100 located in coverage do not overlap theresources of the UE 100-2 itself, the UE 100-2 determines that there isno risk of a collision.

Moreover, for example, when the contents that limit the range of the SAresource area and the data resource area are matching in theconfiguration information and the resource information, the UE 100-2 maydetermine that there is no risk of a collision.

In step S603, the UE 100-2 does not transmit the SA and the D2Dcommunication data using the decided SA resources and the dataresources. The UE 100-2 may decide new SA resources and data resourceson the basis of the resource information.

In step S604, the UE 100-2 transmits the SA using the decided SAresources, and transmits the D2D communication data using the decideddata resources.

As a result of such an operation of the UE 100-2, when D2D communicationis performed around a cell end, it is possible to reduce a collision ofSAs and/or the D2D communication data of the UE 100-2 located out ofcoverage, with SAs and/or the D2D communication data of the UE 100existing in a cell.

Other Embodiments

As described above, the present disclosure has been described with theembodiments. However, it should not be understood that thosedescriptions and drawings constituting a part of the present disclosurelimit the present disclosure. From this disclosure, a variety ofalternate embodiments, examples, and applicable techniques will becomeapparent to one skilled in the art.

For example, in the above-described embodiment, when the UE 100 islocated at the edge of a cell, the UE 100 may transmit resourceinformation received from a cell in which the UE 100 exists, to anotherUE 100. For example, when a reception level of a radio signal from theeNB 200 is within a predetermined range, the UE 100 determines that theUE 100 is located at the edge of a cell. Alternatively, the UE 100 maydetermine whether the UE 100 is located at the edge of a cell by GNSSinformation.

Furthermore, in the above-described embodiment, the UE 100 mayrepeatedly transmit the same SA at a bit level by using the decided SAresources. Specifically, when the decided SA resources are configured bya plurality of control channel elements, the UE 100 transmits the sameSA in each of the plurality of control channel elements.

It is noted that the UE 100 may reduce a bit number of the SA with ahigh priority (for example, an emergency SA), and repeatedly transmitthe SA with a high priority in one SA resource (a resource block).

Furthermore, in the above-described embodiment, the UE 100 mayrepeatedly transmit the same SA in units of resource blocks by using thedecided SA. Specifically, a description will be provided with referenceto FIG. 36. FIG. 36 is a configuration diagram of a radio frame in amobile communication system according to another embodiment.

In FIG. 36, SA 1 a and SA 1 b are the same information and indicate thelocations of the same data resources. Each of the SA 1 a and the SA 1 bindicates the locations of data resources of DATA 11 a to DATA 13 b. TheDATA 11 a and the DATA 11 b are the same D2D communication data, theDATA 12 a and the DATA 12 b are the same D2D communication data, and theDATA 13 a and the DATA 13 b are the same D2D communication data.

It is noted that, in FIG. 36, the UE 100 repeatedly transmits the sameSA in units of resource blocks in a time axis direction; however, thepresent disclosure is not limited thereto. The UE 100 may repeatedlytransmit the same SA in units of resource blocks in a frequency axisdirection.

In the above-described embodiments, each operation example may becombined and executed, where necessary.

In addition, the aforementioned embodiment has described an example inwhich the present disclosure is applied to the LTE system. However, thepresent disclosure is not limited to the LTE system, and may also beapplied to systems other than the LTE system.

APPENDIX (1) Introduction

Resource allocation method with scheduling assignment (SA) for D2Dcommunication was proposed. In this appendix, we consider D2Dcommunication resource allocation with SA from collision avoidanceperspective. In this appendix, we focus on the allocation for out ofcoverage. The similar scheme can be used for in-coverage case as well.However, in-coverage case is not discussed in this appendix.

(2) Design Considerations for D2D Communication Resource AllocationUsing Scheduling Assignments

SA assisted resource allocation provides a possibility of efficientcollision avoidance. There are several advantages of SA.

As discussed, the FIG. 37 shows how UE2 may detect SA1 transmitted byUE1 and use this information to schedule its own data transmissions byavoiding those resources listed in SA1. In order to further improve theabove we propose additional principles for the SA based resourceallocation schemes.

(3) Design Considerations for D2D Communication Resource AllocationRules for Out of Coverage

(3.1) SA Transmissions

In order to reduce receiver complexity SA transmissions are periodic andusing pre-defined time-frequency resources known to the receiver. As anexample, shown in the FIG. 38, the location for SA transmissionresources can be grouped together within a region for simpler detection.

-   -   Proposal 1: If SA is agreed then SAs should be transmitted        periodically and grouped together within a given region.

(3.2) Transmission of Data

In this section a method is described to avoid data collisions. Each SAis mapped to a certain set of time-frequency resources that can be usedfor data transmissions. Each D2D is allowed to select a resource for itsSA transmission as described in the above section. However, the same D2DUE can only transmit its data in resources that are associated with theSA resource location. In other words, the location of the SA determinesthe location of the data transmission resources. As shown in the FIG.39, SA1 and SA2 points to data 11, 12, 13 and data 21, 22, 23respectively. This method avoids collisions between data transmissions.

-   -   Proposal 2: In order to avoid data collisions SA is mapped to a        certain set of time-frequency resources that can be used for        data transmissions.

(3.3) Reduction in Collision of SA Transmissions

The above method describes the allocation of data transmissions using SAas a pointer. However, the above method is not sufficient to avoidcollisions between SA transmissions. In this section we present a methodto reduce SA transmission collisions. Each D2D UE monitors the SA regionto detect SA transmitted by the other D2D UEs. Using this informationthe same D2D UE avoids transmitting its SA in the same resource used byother D2D UEs during the previous SA transmissions. For example, asshown in FIG. 40, UE1 and UE2 transmit SA11 and SA21 respectively. Athird D2D UE (not shown in the figure) detects those transmissions andthen transmits its SA32 at a different location. UE1 and UE2 can use thesame resources used in the previous iteration for SA12 and SA22,respectively. In the initial first SA period UE1 and UE2 can randomlyselect resources for SA transmissions.

-   -   Proposal 3: If SA is agreed then to reduce SA collisions, D2D UE        avoids transmitting its SA in the same resource used by the        other D2D UEs in the previous SA transmissions.    -   Proposal 4: If SA is agreed, and then the resources for the        initial SA transmissions are randomly selected in the SA region.

In addition, the entire content of is incorporated in the presentspecification by reference.

As described above, the mobile communication system and the userterminal according to the present disclosure are able to efficientlyscan control information, and thus they are useful in a mobilecommunication field.

The invention claimed is:
 1. A first user terminal, comprising: at leastone processor and at least one memory coupled to the at least oneprocessor, wherein the at least one processor is configured to performprocesses of: determining a plurality of first radio resources to beused for transmitting control information from the first user terminalto a second user terminal; and directly transmitting the controlinformation to the second user terminal in each of the plurality offirst radio resources, by Device-to-Device (D2D) communication, thecontrol information is included in each of the plurality of first radioresources, and the control information transmitted in each of theplurality of first radio resources indicates a same at least onesubframe of second radio resources to be used for transmitting data bythe D2D communication.
 2. The first user terminal according to claim 1,wherein the at least one processor is configured to perform the processof randomly determining the plurality of first radio resources from aresource area in which radio resources, which are able to be used fortransmitting the control information, are arranged.
 3. The first userterminal according to claim 1, wherein the at least one processor isconfigured to perform a process of receiving information on theplurality of first radio resources from a base station.
 4. The firstuser terminal according to claim 3, wherein the at least one processoris configured to perform the process of receiving the information bydownlink control information from the base station.
 5. The first userterminal according to claim 3, wherein the at least one processor isconfigured to perform the process of receiving the information by aRadio Resource Control (RRC) message from the base station.
 6. The firstuser terminal according to claim 3, wherein the at least one processoris configured to perform the process of transmitting the information ifthe first user terminal exists in a cell managed by the base station. 7.An apparatus for a first user terminal comprising: at least oneprocessor and at least one memory coupled to the at least one processor,wherein the at least one processor is configured to perform processesof: determining a plurality of first radio resources to be used fortransmitting control information from the first user terminal to asecond user terminal; and directly transmitting the control informationto the second user terminal in each of the plurality of first radioresources, by Device-to-Device (D2D) communication, the controlinformation is included in each of the plurality of first radioresources, each of first radio resources comprises one resource block,and the control information transmitted in each of the plurality offirst radio resources indicates a same at least one subframe of secondresources to be used for transmitting data by the D2D communication. 8.The first user terminal according to claim 1, wherein each of firstradio resources comprises one resource block.
 9. A first user terminal,comprising: at least one processor and at least one memory coupled tothe at least one processor, wherein sets of radio resources are arrangedby repeating a set of radio resources in a time direction, the a set ofradio resources being for control information of Device-to-Device (D2D)communication and for data corresponding to the control information, theat least one processor is configured to perform processes of:determining a plurality of first radio resources within a first setincluded in the sets of radio resources, wherein the plurality of firstradio resources is to be used for transmitting first control informationfrom the first user terminal to a second user terminal; and directlytransmitting the first control information to the second user terminalin each of the plurality of first radio resources by the D2Dcommunication, the first control information is included in each of theplurality of first radio resources within the first set, the firstcontrol information transmitted in each of the plurality of first radioresources indicates a same at least one subframe of second radioresources within the first set, to be used for transmitting first databy the (D2D) communication, and the at least one processor is configuredto perform processes of directly transmitting the first data by the D2Dcommunication by using the second radio resources within the first set.